Pressure sensor, method of producing the sensor, and in-cylinder pressure detection structure of internal combustion engine

Abstract

In a pressure sensor A according to the presenting invention, a piezoelectric element B formed by a thin film of aluminium nitride is mounted on a base material C of an insulating material, and output electrodes D and E and output lead wires F and G which transmit a signal detected by the piezoelectric element B are mounted on the side of the base material C. The pressure sensor A is directly mounted on a cylinder head e of an internal combustion engine, or is mounted on the outer surface of a heater L which is secured at the free end of a glow plug K, whereby it is disposed to face a combustion chamber h. A combustion pressure or oscillations during the operation of the engine can be detected with a high sensitivity.

Description

TECHNICAL FIELD [0001] The present invention relates to a pressure sensor, for example, a pressure sensor installed within a cylinder of an internal combustion engine for detecting a combustion pressure and oscillations within the cylinder during operation of the engine. The invention also relates to a method of manufacturing such a pressure sensor and to a structure utilizing the pressure sensor for detecting cylinder internal pressure of the internal combustion engine. BACKGROUND ART [0002] A variety of power train control techniques are used in an internal combustion engine with an intent to cope with the purification of exhaust gases and a compatible attainment of improvements in the fuel cost and the engine performance. If it were possible to detect a change in the combustion pressure within the cylinder exactly and to detect a manner of injection from an injector exactly, an optimum control of ignition timing, a more precise control of fuel injection and a rapid accommodation ...

AI Technical Summary

Benefits of technology

[0017] The pressure sensor according to this invention is arranged so that a signal transmitting means which conveys a signal from the piezoelectric material in the form of a thin film and formed of a material such as a nitride or oxide is passed through the base material to be taken externally. Accordingly, when used in an environment such as within a combustion chamber of an internal combustion engine, a sufficient durability is secured, permitting a combustion pressure or oscillations to be detected with a high accuracy. Because the piezoelectric element is in the form of a thin film and can be in a compact form, a high freedom of installation is obtained, allowing a detection of a combustion pressure with a very high accuracy and a detection of a manner of injection from an injector.

[0019] In the structure for detecting a cylinder internal pressure of an internal combustion engine according to this invention, the piezoelectric element is disposed within the combustion chamber of the internal combustion engine, and accordingly, as soon as the internal combustion engine is started and the combustion is initiated, the pressure sensor detects the pressures and oscillations which are generated attendant to the combustion, but because the pressure sensor is mounted on a portion of a free end of a housing which faces the interior of the combustion chamber, the sensitivity of the pressure sensor is very high in comparison to the prior art arrangement, permitting a timing of the incipiency of ignition, a condition of combustion or a fuel injection pressure or the like to be detected with a high accuracy.

[0021] In the structure for detecting a cylinder internal pressure of an internal combustion engine according to this invention, an auxiliary part which is normally mounted on an internal combustion engine is used to dispose the pressure sensor within the combustion chamber of the internal combustion engine, thus dispensing with a mounting space on the cylinder head while facilitating a mounting and a replacement with a very slight cost-up. A combustion pressure or a manner of a fuel injection can be precisely detected with a high sensitivity without degrading the performance of the engine, an ignition plug or an injector. Since the timing of incipiency of an ignition or a manner of fuel injection can be exactly detected, a more optimum ignition timing control and a more precise fuel injection control can be performed. The fuel injection control and the ignition timing control which take place in an optimum manner enables a saving of the fuel cost, a low emission and an improvement of the engine performance.

Problems solved by technology

Accordingly, when the pressure sensor is installed within a combustion chamber of an internal combustion engine, for example, signal transmitting means such as the electrode and an output lead wire, not shown, are directly exposed to a high temperature environment within the combustion chamber, causing a problem of the durability.

In addition, if a carbon is deposited during use over a prolonged period of time, there is a likelihood that a conduction may occur between the both electrodes.

In particular, there remains a problem that it is difficult to catch the timing of initiation of the ignition exactly.

However, it is subject to friction heating between the sheath and the housing, and it cannot be evaluated as exhibiting an excellent accuracy of detection.

In addition, there is a tendency that the interior of the housing assumes a high pressure, presenting a likelihood of presenting a problem in respect of the durability as a result of a failure of a hermetic seal of the sheath and the breakage of the heater.

In the pressure sensor for an internal combustion engine disclosed in the fourth citation (Japanese Laid-Open Patent Application No. 2001-108,556), the sensor is mounted externally of the cylinder head in the similar manner as the plug internally housing the pressure sensor as disclosed in the first citation, and therefore it is difficult to catch a change in the combustion pressure exactly.

In addition, as for detecting the oscillations during the injection of the fuel, a distance from the injection port is too far to provide a sufficient accuracy for the sensor which is intended to detect an abnormality.

Finally, with respect to the plug internally housing the pressure sensor, the glow plug with an ignition sensor and the piezoelectric element in the pressure sensor for an internal combustion engine which are disclosed in the second to the fourth citation, the freedom of installation is limited, and it is difficult to install such sensor at a location which enables the detection of a combustion pressure or a fuel injection pressure with a high accuracy.

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